One example of a rotary wing aircraft is a helicopter.
FR 2,949,432 (D1) proposes such a device, in the case at hand a damper designed to be installed on a rotary wing aircraft rotor.
The solution considered in this document consists of providing a single chamber within an elastomer layer.
Two embodiments of the damper are shown by FIG. 1 and FIG. 2, respectively.
This damper 100′ comprises two frame elements 100′A, 100′B each intended to be mounted on one of the parts of a rotary wing aircraft.
In FIG. 1, the damper 100′ comprises an elastomer layer 101′ positioned between the two frame elements 100′A, 100′B and a single chamber 102′ positioned within the elastomer layer 101′. The single chamber 102′ is filled with colored liquid. The single chamber 102′ is positioned at a predetermined distance DIM1, DIM2 from one and/or the other of the ends E′1, E′2 of the elastomer layer.
Under the effect of the repeated relative movement of the parts of the rotary wing aircraft rotor, one or more crack(s) spread from at least one of the ends E′1, E′2 of the elastomer layer 101′ toward the single chamber 102′. This crack is characteristic of fatigue-related damage of the elastomer layer 101′.
When this crack reaches the single chamber 102′, the colored liquid contained in the single chamber passes through the crack and tends to leave the damper 100′.
Thus, during a maintenance operation, a technician can become aware of the liquid leak outside the single chamber 102′ and deduce therefrom that the part must be changed.
As a result, the solution proposed in document D1 prevents a maintenance technician from taking a depth and/or width measurement of the crack.
Furthermore, inasmuch as the single chamber 102′ has an annular section going all the way around the elastomer layer around its longitudinal axis, one ensures that any crack spreading from at least one of the ends E′1 and E′2 of the elastomer layer 101′ toward the single chamber 102′ is able to reach this single chamber 102′.
However, the presence of this single chamber 102′, which has an annular section going all the way around the elastomer layer around its longitudinal axis, alters the mechanical properties, in particular the dynamic properties, of the damper 100′, relative to a traditional damper (i.e., without a chamber like that proposed in document D1, all other things being equal, in particular regarding its dimensions).
The presence of such a chamber 102′ can also have a negative impact on the lifetime (fatigue) of the damper.
The alteration of the mechanical properties can be accentuated, relative to such a traditional damper, when the single chamber 102′ furthermore splits the elastomer layer 102′ into two separate parts 101′A, 101′B, as shown in FIG. 2.
This can also have a negative impact on the lifetime (fatigue) of the damper.